1. Field of the Invention
The present disclosure relates to a liquid crystal display device, more particularly, to a liquid crystal display device capable of improving a contrast ratio and of reducing a halo phenomenon with low power consumption, and a method for local dimming driving the same.
2. Discussion of the Related Art
Recently, flat panel display devices including liquid crystal display (LCD) devices, plasma display panels (PDP) and organic light emitting diodes (OLED) have been used extensively.
Such a LCD device includes a liquid crystal panel for displaying an image via pixel matrixes which uses electric and optical properties of liquid crystal having anisotropy with respect to refractivity and permittivity, a driving circuit for driving the liquid panel and a backlight unit for projecting a light toward the liquid crystal panel. Each of pixels provided in the liquid crystal display presents gradation by adjusting transmissivity of lights transmitted via the liquid crystal panel and a polarization plate from the backlight unit by variation of a liquid crystal arrangement direction based on a data signal.
Brightness of each pixel provided in the LCD device is determined by multiplication of light transmittance of the liquid based on brightness and data of the backlight unit. To improve a contrast ratio and to reduce power consumption, the LCD device analyzes an input image and adjusts a dimming value to control the brightness of the backlight. Also, the LCD uses backlight dimming which can compensate data. For example, a dimming value is decreased to decrease the backlight brightness decreased and data compensation increases brightness, according to a method for backlight dimming to reduce power consumption.
Recently, a light emitting diode (LED) has been used as light source the backlight unit, because the LED has an advantage of high brightness with low power consumption in comparison to a conventional lamp. It is possible to control brightness at each position in an LED backlight unit and the LED backlight unit may be driven in Local Dimming which controls brightness for each of divided light-emitting blocks. Local Dimming analyzes image data for each of light-emitting blocks and it determines a local dimming value, such that the brightness of the LED backlight may be controlled for each of the blocks based on the determined local dimming value and that the image data may be compensated. As a result, Local Dimming can improve a contrast ratio and reduce more power consumption.
However, Local Dimming has a disadvantage of halo which occurs because of combination of dimming difference among the light-emitting blocks and a dark screen. For example, if displaying according to Local Dimming an image having a bright (high) gradation object located in quite a dark (low) gradation background as shown in FIG. 1, dimming difference between bright blocks and dark blocks might generate halo in the dark block near the blocks displaying the bright object. Because of the halo, screen quality happens to deteriorate.